The present invention relates to a coded picture signal requantization system for high efficiency coding of picture signals of television transmission, video conference, video telephone and so forth.
The simplest method that has been employed for decreasing the total number of coding bits is to roughly sample picture signals for thinned-out coding of a picture and to interpolate the thinned-out picture elements during decoding. For example, by thinning out every other picture element in one line and thinning out every other line, the number of picture elements to be coded is reduced down to 1/4, permitting the reduction of the number of bits required for coding down to 1/4.
With the above method, however, resolution of the picture signal is impaired, resulting in blurring of the decoded picture.
Conventionally known as a solution to this problem is a system called a "two-channel coder" (W. F. Schreiber et al., "A Two-Channel Picture Coding System", IEEE Transactions on Communications, December 1981, Vol. COM. 29, Nr. 12, P 1841-P 1858). This method is characterized by separating picture signals into high-frequency and low-frequency components for coding. In this case, it is also possible to reproduce the low-frequency component of the picture by thinned-out picture signals, and it can also be considered that the high-frequency component of the picture contains information for providing resolution of the picture, such as an edge or the like. However, this method does not involve adaptive quantization.